Electronic annunciator



Oct. 4, 1955 c. A. SCHURR 2,719,966

ELECTRONIC ANNUNCIATOR Filed Nov. 1, 1951 5 Sheets-Sheet 1 I N V EN TOR.(H/1245s ALLAN So /wee Oct. 4, 1955 Filed Nov. 1, 1951 C. A. SCHURRELECTRONIC ANNUNCIATOR 3 Sheets-Sheet 2 United States Patent ELECTRONICANN UNCIATOR Charles Allan Schurr, Euclid, Ohio, assignor to TheElectric Controller & Manufacturing Company, Cleveland, Ohio, acorporation of Ohio Application November 1, 1951, Serial No. 254,321 18Claims. (Cl. 340-453) This invention relates to an electronicannunciator and more particularly to an electronic annunciator havingmany different uses but eminently suitable for indicating which, if any,of a plurality of protective contacts in an undervoltage protectioncircuit for a motor opened to stop the motor.

l-leretofore, electromagnetic annunciators having movable indicatingflags or vanes have been used with industrial motor controllers toindicate which specific one, or ones, of several protective contacts inseries with an undervoltage relay opened to cause the relay to shut downthe machine driven by the motor. The time required to locate the causeof the shutdown is thereby greatly reduced, particularly when some ofthe contacts which could have caused the shutdown are located in widelyseparated locations or some are of the type that immediately recloseafter opening so that no indication that they had opened is otherwiseavailable. In fact, some system of contact opening indication has becomealmost an economic necessity for many complex electrically drivenindustrial machines because of the large number of widely separatedprotective contacts required and the high cost of any extended shutdown.Although the prior electromagnetic annunciators can be made to performsatisfactorily, their relatively high cost and large size makes itdesirable to provide a less expensive and more compact annunciator.

An electronic annunciator in accordance with the present invention usesonly inexpensive and conventional electrical components of very smallsize and therefore is more compact and less expensive than priorelectromagnetic annunciators. Furthermore, the present annunciator iscapable of giving a positive indication of the opening of one or moreprotective contacts in undervoltage protection circuits of relativelylow inductance, is operative irrespective of whether the protectivecontacts are on the negative or positive side of the undervoltage relayand whether or not the cont-acts are in the same or difierent circuits,and retains its initial indication until manually reset even thoughother of the protective contacts had been subsequently opened or theopened contact had reclosed.

It is an object of this invention to provide an annunciator having theforegoing advantages.

Another object is to provide an annunciator which is electronicallyoperated.

Another object is to provide an electronic annunciator in which avoltage surge upon opening of a contact causes the ignition of a gaseousdischarge tube.

Another object is to provide an electronic annunciator in which the glowof an ignited gaseous discharge tube may be used as the indicatingmedium.

Among other objects is the provision of electronic annunciators in whicha three-element, gaseous discharge tube has its control electrodeconnected so as to become operative to initiate ignition of the tubeupon occurrence of a voltage surge across a contact; or in which a threeelement, cold cathode, gaseous discharge tube has its starter or triggerelectrode connected so as to become operative to cause ignition of thetube upon opening of a contact; or in which a plurality of two-element,gaseous discharge tubes are fired selectively by changes in thepotential of capacitors respective to the tubes; or in which the starteror trigger electrode of a three-element, cold cathode, gaseous dischargetube is coupled to a contact through a transformer and responds when thecontact opens to cause ignition of the tube, or in which the pairs ofelectrodes of a plurality of two-element, cold cathode, gaseousdischarge devices are connected in respective loop circuits eachincluding a contact and a capacitor.

Additional objects are to provide an electronic annunciator capable ofindicating which of a plurality of contacts opened whether the contactsare in the same or separate circuits and to provide an electronicannunciator capable of being supplied from either an alternating or adirect current source.

In one illustrated embodiment of this invention, a plurality ofidentical, cold cathode, three-element, gaseous discharge devices ortubes are connected in parallel across a portion of a voltage divider sothat a voltage is impressed between their respective plates andcathodes. This voltage is less than that required to initiate an arcdischarge between the plates and cathodes of the tubes but is sufiicientto maintain such a discharge after it has been initiated. A plurality oftransformers have their primary windings connected in respective loopcircuits each of which includes one of a plurality of protectivecontacts that are interposed in an undervoltage protection circuit inseries with each other and with an operating winding of anelectromagnetic undervoltage relay. The secondary windings of thetransformers are connected between the trigger electrodes and cathodesof the tubes, respectively. Upon opening of any of the protectivecontacts, a current flows momentarily through the primary of itsassociated transformer. The resulting voltage surge in the secondary ofthat transformer is applied to its associated trigger electrode causingit to become sufficiently positive with respect to its associatedcathode to initiate an arc discharge that continues between the cathodeand plate of the corresponding one of the tubes. This are discharge isreadily visible and provides an indication as to which one of theseveral contacts opened. The cathode-plate circuits of the tubes may beopened manually at any time to extinguish those of the tubes which havebeen ignited.

In another illustrated embodiment of this invention, two element, coldcathode, gaseous discharge devices or tubes are used instead ofthree-element tubes and are connected in respective loop circuits withthe protective contacts, suitable capacitors being inserted in the loopcircuits, re spectively. Upon opening of any one of the contacts, theside of the opened contact nearest the positive supply conductorsuddenly changes from the potential of the negative supply conductor tothe potential of the positive supply conductor. Since the voltage acrossa capacitor cannot change instantaneously, there is a sudden increase inthe potential across the electrodes of the tube associated with the oneof the contacts that has opened, and that tube accordingly breaks downand emits a visible glow. When the contact that opened recloses, theignited tube is not extinguished because the resulting voltage surge issubstantially absorbed by a suitable resistor and the now lowerresistance of the conducting tube. The ignited tube may be extinguishedby opening of a reset switch. Thus the annunciators operate by employingthe characteristics of gaseous discharge tubes by which a visibledischarge is initiated by a surge in voltage resulting from opening ofan inductive circuit and continues thereafter at voltage below the surgevalue.

Further objects and advantages of this invention will become apparentfrom the following description wherein reference is made to thedrawings, in which:

Fig. l is a front elevation of the indicating portion of an electronicannunciator in accordance with this invention,

Fig. 2 is a section taken along the line 22 of Fig. 1,

Fig. 3 is a wiring diagram of an electronic annunciator in accordancewith this invention which may have its indicating tubes arranged asshown in Figs. 1 and 2,

Figs. 4 and 5 illustrate modifications of the annunciator of Fig. 3,

Fig. 6 is a Wiring diagram showing how the annunciators of Figs. 3 and 4may be used to indicate the operation of contacts in separate circuits,

Fig. 7 shows how an annunciator in accordance with this invention may beused with an alternating current source, and

Fig. 8 illustrates a further modified annunciator.

Referring to Figs. 1 and 2, a suitable panel 10 has a plurality ofhorizontally aligned circular openings 11 behind which a plurality ofgaseous discharge devices or tubes 12, each having a transparentenvelope, are respectively mounted. Thus, when any one of the tubes 12becomes ignited, its glow is visible from the front of the panel 10through its associated one of the openings 11. Preferably, the tubes 12are mounted in respective sockets 13 carried by a bracket 14 attached tothe rear of the panel 10. Suitable indicia 15 may be placed on the frontof the panel beneath the openings to identify each of the tubes 12 inrelation to a specific one of a plurality of protective contacts withwhich the tubes 12 are operatively associated in a manner to bedescribed. The indicia 15 may be a simple numbering system as shown orthe name of each of the contacts and its physical location may beinscribed on the panel.

Referring now to Fig. 3, conductors 16 and 17 are arranged to beconnected respectively to a positive supply conductor 18 and a negativesupply conductor 19 of a source of direct current (not shown) by meansof a suit able switch such as a knife switch 20. A conventionalthree-speed point, reversing master switch 21, illustrated in developedform, has an off-point segment 22 which,

only when the master switch 21 is in the off position, cornpletes anundervoltage protection circuit from the conductor 16 to the conductor17 through a conductor 24, an operating winding 25w of anelectromagnetic undervoltage relay 25 having a normally open contact25a, and through a plurality of protective contacts 26, 27, and 28connected in series with each other and with the winding 25w. As shown,the winding 25w is interposed on the negative side of the contact 26 andon the positive side of the contacts 27 and 28, but the winding 25w andthe contacts 26, 27, and 28 may be arranged in any other order ifdesired.

The relay 25 is operatively energized and its contact 25a is closed ifthe master switch 21 is in the off-position, the knife switch and all ofcontacts 26, 27, and 28 are closed, and an adequate voltage existsbetween the conductors 18 and 19. The relay when operatively energizedcompletes its own holding circuit through its contact 25:: and aconductor 29 from the conductor 16 to the contact 26. The holdingcircuit bypasses the conductor 24 and the segment 22 and serves tomaintain the relay 25 in its operated position when the master switch 21is moved in either direction from the off-position.

Additional segments 30 of the master switch 21 are connected to theconductor 16 through a conductor 31, the conductor 24, and the segment22 when the master switch is in the off-position, and are connected tothe conductor 16 through the conductors 31 and 29 when the master switch21 is in any of its operating positions and the contact 25a is closed.The segments 30 may be arranged to control the operation of suitableelectromagnetic switches (not shown) of a controller 32 for an electrictranslating device such as a motor 33 having an armature winding 34 anda field winding 35 and arranged to be supplied with power throughconductors 36 which may be connected to the same source as theconductors 18 and 19. It will be understood that the undervoltage relay25 and one or more of the contacts 26, 27, and 28 may be included in thecontroller 32.

The particular undervoltage protection circuit and master switcharrangement illustrated in Fig. 3 is indicative of conventional practicefor providing undervoltage protection in a motor controller. Forexample, should the voltage at the conductors 18 and 19 decreases belowthe drop-out value of the relay 25 or any one or more of the contacts26, 27, or 28 open momentarily, the contact 25a opens. If the masterswitch 21 is in any of its operating positions, opening of the contact25a disconnects the segments 30 from the conductor 16 and the controller32 operates to deenergize the motor 33. It is then necessary to returnthe master switch 21 to the oif-position before the segments 30 can beconnected again to the conductor 16 to permit the motor 33 to berestarted.

The contacts 27 and 28 are shown as normally closed and the contact 26is shown as normally open, but when conditions are proper for operationof the motor 33, all of the contacts 26, 27, and 28 are closed. Althoughonly three protective contacts 26, 27, and 28 are illustrated, it is tobe understood that any number of normally open or normally closedcontacts may be provided, as many as twenty or more not being uncommon.Exemplary functions for contacts such as the contacts 26, 27, and 28 areto provide protection against overloading of the motor 33, overtravel oroverspeed of a machine driven by the motor, low oil pressure, stoppingof a related machine, and the like.

So long as all of the contacts 26, 2'7, and 28 are closed, operation isnormal and may proceed, but if any one or more of these contacts open,abnormal conditions have occurred and the motor 33 is deenergizedautomatically and brought to a stop. In order to restart the motor,after a stoppage for this reason, it is necessary to return the masterswitch 21 from an operating position to the off-position in order toreset the undervoltage relay 25. Many protective contacts such as thecontacts 26, 27, and 28 are often of the type that immediately recloseafter they have opened, and hence give no indication of their operation,and some may be located at remote points. Hence, it often requiresconsiderable time merely to discover which of the several protectivecontacts opened to cause the motor to stop. Since it is undesirable torestart the motor 32 until the cause of its automatic stoppage isascertained and corrected if necessary, considerable time often elapsesbefore an attempt should be made to restart the motor 33 even though thecause of the shutdown when once determined can be quickly corrected. Theannunciator now to be described is combined with the undervoltageprotection circuit to provide a readily visible indication at a singlelocation as to which of the protective contacts 26, 27, and 28 opened tostop the motor 33 thereby permitting more rapid discovery of the causeof stoppage.

The annunciator, as illustrated in Fig. 3, comprises a plurality ofvoltage transferring means in the form of transformers 41, 42, and 43,preferably of the iron core type, having their respective primarywindings 41p, 42p, and 43p connected inloop circuits with the contacts26, 27, and 28, respectively, by respectivecoupling means which includeresistors 45, 46, and 47, respectively. The resistance of each of theresistors 45, 46, and 47 is so selected with respect to the resistanceof its associated primary winding 41p, 42p, or 43p that, when itsassociated one of the contacts 26, 27, or 28 opens and the next highestexpected voltage is at the conductors 18 and 19, the relay 25 opens itscontact 25a. In fact, it is possible and preferable to make theresistance of the resistors 45, 46, and 47 so high that the current thatflows to the winding 25w when any one of them is operatively in thecircuit is insignificantly small as compared to the drop-out current ofthe relay 25.

A plurality of gaseous discharge tubes 48, 49, and 50 are arranged to beresponsive to the voltage across the con tacts 26, 27, and 23,respectively. Preferably, the tubes 48, 49, and 50 are cold cathode,three-element, gaseous discharge tubes containing respective plates oranodes 48p, 49p, and 5-9;), cathodes 48c, 49c, and 500, and starter ortrigger electrodes 43, 49;, and Silt. The gas filling is usually neon,argon, or krypton, each of these gases giving a characteristicallycolored glow upon ignition of the tube. The envelopes of the tubes aretransparent so that the glow is visible and can serve as an indicationof the ignition or non-ignition of the tube. In the operation of tubesof this type, a relatively small amount of electrical energy supplied tothe starter electrode initiates an arc discharge between the cathode andstarter electrode which in turn initiates a much greater dischargebetween the cathode and main anode. In tubes of this type which are atpresent commercially available, known as the OA4G and 5823, a startingpotential of at least about 85 to 100 volts preferably applied through aresistance of not more than one-half megohm is required. As mentioned,the tubes 48, 49, and 50 have transparent envelopes so that theirinternal glow is visible, and preferably are mounted in a singlelocation in the manner of the tubes 12 of Figs. 1 and 2.

The transformers 41, 42, and 43 have secondary windings 41s, 42s, and43s, one terminal of each of which is connected to the conductor 1'7 andthe other terminals of which are connected respectively to the triggerelectrodes 48t, 491, and 502.

A voltage divider 51 comprising a pair of series connected resistors 52and 54 is arranged to be connected across the conductors 16 and 17through a normallyclosed push button 55 interposed between the resistor52 and the conductor 16. Either one or both of the resistors 52 and 54may be made adjustable if desired. A junction point 56 intermediate ofthe resistors 52 and 54 is connected to a common terminal of parallelcircuits including operating windings 58w of respective relays 58 andthe plates 48p, 49p, and 50 respectively. The cathodes 48c, 49c, and 500are each connected directly to the conductor 17. Preferably theresistors 52 and 54 are selected so that when none of the tubes 48, 49,and St is ignited, the voltage across the resistor 54 and thus betweenthe respective cathode and plates of the tubes is approximately midwaybetween the potential required to initiate an arc discharge between thecathodes and plates and the extinction potential of such discharge.

The operation of the circuit of Fig. 3 may be explained by assuming thatthe relay 25 is in its operated position 6 with its contact 2511 closedand the master switch 21 is in one of its operating positions. Shouldany one or more or the contacts 26, 27, and 28 open momentarily at thistime and then either stay open or reclose, the relay 25 drops out toopen the contact 25a which removes power from segments 30 of the masterswitch 21 which in turn causes the controller 32 to effectdeenergization of the motor 33. The motor 33 accordingly slows down andstops and cannot be reenergized unless the master switch 21 is firstreturned to the off-position. The relay 25 operates to close its contact25a when the master switch 21 reaches the off-position, provided all ofthe protective contacts which opened have reclosed, but the masterswitch 21 should not be moved again to an operative position until thecause of the shutdown is ascertained and cor rected if necessary.

The annunciator portion of the circuit of Fig. 3 provides a readilyvisible indication as to which one or which ones of the contacts 26,2'7, or 28 opened. This is because, upon opening of any of the contacts26, 27, and 28, current starts to flow through the one or more of theprimary windings 41p, 42p, and 43p which are associated with the openedcontact or contacts. Because of the inductance of the winding 25w, thiscurrent is for an instant relatively large, but, because one or more ofthe resistors 45, 46, and 47 are now effectively in series with thewinding 25w, soon decreases to a value insufiicient to maintain therelay 25 in its operated position or to pick up the relay 25 when themaster switch 21 is returned to the off-position. However, the currentsurge around the opened one of the contacts 26, 27, and 28 is suflicientto induce a voltage in the secondary of its associated transformer whichcauses ignition of the appropriate one of the tubes 48, 49, and 50, theother tubes remaining unignited.

For example, assuming that the contact 27 opened, the current surge inthe primary winding 42p is sufficient to induce a voltage in thesecondary winding 42s which causes the trigger electrode 49t to becomesutficiently more positive than the cathode 490 to cause ignition of thetube 49. Once ignited, the tube 49 remains ignited and produces avisible glow due to current flowing (electron sense) from the negativeconductor 17, through the cathode 490, this plate 49p, one of thewindings 58w, the resistor 52, and the push button 55 to the positiveconductor 16. The tube 49 by its characteristic glow thus indicatesthat, of the several contacts 26, 27, and 28, the contact 27 in thisinstance opened and caused opening of the contact 25a and consequentshutdown of the machine driven by the motor 33. The one of the relays 58in series with the tube 49 is picked up by the plate current of the tubeand any suitable device operated by this relay 58 may also be used toindicate that, of the several contacts, it was the contact 27 thatopened. Upon drop out of the relay 25, the master switch 21 should bereturned to its off-position.

After checking the cause of opening of the contact 27, correcting anyfault, if necessary, and reclosing of the contact 27, if necessary, themaster switch 21 may be moved again to an operative position so as torestart the motor 33. At any time prior to or after resumption ofoperation, the push button 55 may be opened momentarily to extinguishthe tube 49 and to de-energize the energized one of the relays 58.

Had the contacts 26 or 28 opened instead of the contact 27, the tubes 48or 56 would have become ignited instead of the tube 49. If more than oneof the contacts 26, 27, and 28 opened instead of but one, theappropriate tubes in each instance would have become ignited. Since thetubes 48, 49, and 50 may be grouped at a single location and providedwith suitable indicia, for example, in the manner illustrated in Figs. 1and 2, the glow produced by any one of the tubes immediately shows whichof the several contacts 26, 27, and 28 opened to stop the machine drivenby the motor 33. Devices operated by the several relays 58,respectively, also may be grouped at a single location to provide suchindication if desired.

Fig. 4 illustrates modifications which may be made in the completecircuit of Fig. 3. Elements in Fig. 4 which are the same as those ofFig. 3 are referred to by the same reference numerals. Referring to Fig.4, the resistors 45, 46, and 47 of Fig. 3 are replaced by pairs ofcapacitors 61, 62, and 63 and the transformers 41, 42, and 43 of Fig. 3are replaced by transformers 64, 65, and 66 which may be of the air coretype, and which have primary windings 64p, 65p, and 66p, respectively,and secondary windings 64s, 65s, and 66s, respectively. The individualcapacitors of the pair of capacitors 61 are arranged in series, one oneach side of the primary winding 64p, and the capacitors 62 and 63 aresimilarly arranged in the loop circuits including the primary windings65p and 66p and the contacts 27 and 28, respectively. Suitable resistors67 may be interposed respectively between the secondary windings 64s,65s, and 66s and their associated trigger electrodes 481, 491, and SW.

As mentioned, the resistors 45, 46, and 47 of Fig. 3 must be of suchvalue that when any one of the contacts 26, 27, or 28 opens, the currentflowing in the resistor associated with the open contact must becomeless than the drop-out value of the relay 25 when the voltage at thesupply conductors 18 and 19 is at its highest value. In Fig. 4, on theother hand, when one of the contacts 26, 27, or 28 opens, a momentarycharging current flows through the associated pair of the capacitors 61,62, and 63. This charging current is suflicient to cause a voltage surgein the secondary winding 64s, 65s, or 66s capable of causing ignition ofthe appropriate one of the tubes 48, 49, or 50. The charging currentmomentarily is also sufficient to hold the relay 25 in its operatedposition, but after the lapse of a few micro-seconds, it decreases belowthe drop-out value of the relay 25 and thereafter reaches zero.Accordingly, the relay 25 in Fig. 4 drops out after a very slight timedelay and thereafter its winding 25w is completely deenergized. Ifdesired, only one capacitor may be interposed in each of the loopcircuits, but two are preferable to provide protection againstaccidental short circuiting of one. It will also be understood thatadditional protection against failure of the capacitors could beprovided by using, in addition, current limiting resistors such as theresistors 45, 46, and 47 of Fig. 3.

In the circuit as shown in Fig. 4, the relay 58 of Fig. 3 have beenreplaced by resistors 68, the glow of the tubes 48, 49, and 50 onlybeing used in this instance to indicate which of the contacts 26, 27,and 28 operated. Also, in Fig. 4 the relay winding 25w is illustrated onthe positive side of all of the contacts 26, 27, and 28. It will beunderstood that either or both of these last two changes may be made inFig. 3 if desired.

Fig. also illustrates a modified annunciatorwhich also may be used withthe un'dervoltage protection circuit of Fig. 3.

Referring to Fig. 5, a plurality of two-element, cold cathode, gaseousdischarge tubes 71, 72, and 73 having transparent envelopes areconnected in respective loop circuits including the protective contacts26, 27, and 28, respectively. The loop circuit including the contact 26and the tube 71 also includes, in series, a coupling means in the formof a resistor 74 and a voltage transferring means in the form of acapacitor 75. Similarly, the loop circuit including the contact 27includes a series-connected resistor 76 and a capacitor 77, and the loopcircuit including the contact 28 and the tube 73 includes aseries-connected resistor 78 and a capacitor 79'. The tubes 71, 72, and73 have plates 71p, 72p, and 73 which are connected to the positive sideof their associated contacts 26, 27, and 28 through the capacitors 75,77, and 79, respectively, and the resistors 74, 76, and 78,respectively, and have cathodes 71c, 72c, and 730, respectively, whichare connected to the negative side of their associated contacts 26, 27,and 28. Each of the tubes 71, 72, and 73 should have a relatively largedifferential between its ignition and extinction potential. If desired,the tubes 71, 72, and 73 may be the same as the tubes 48, 49, and 50 butarranged to operate as two-element tubes with the trigger electrodes48!, 49t, and 501 connected directly to their respective cathodes 48c,49c, and 500.

The voltage divider 51 including the series connected resistors 52 and54 is connected between the conductors 16 and 17 with the reset switch55 interposed between the resistor 52 and the conductor 16. The platecircuits of the respective tubes 71, 72, and 73 are completed betweenthe conductor 17 and the junction point 56 between the resistors 52 and54 in series with respective resistors 84.

With all of the tubes 71, 72, and 73 extinguished, the voltage acrossthe resistor 54 is preferably intermediate between the extinction andignition potential of tubes, and, if all of the contacts 26, 27, and 28are closed, the capacitors 75, 77, and 79 become charged to the value ofthis voltage. Upon opening of one of the contacts 26, 27, or 28, forexample, the contact 27, the side of the contact 27 nearest to the relaywinding 25w suddenly changes from the potential of the negative supplyconductor 17 to that of the positive supply conductor 16. Since thevoltage across a capacitor cannot change instantaneously, there is asudden increase in voltage at the plate 72p of the tube 72. The cathode72c of the tube 72, however, remains at the potential of the negativeconductor 17. This voltage ditterence is sutficient to cause the tube 72to break down and emit a visible glow, and it remains ignited by thecurrent flowing through its plate circuit and the associated one of theresistors 84. When the contact 27 again recloses, the tube 72 does notbecome extinguished because the resulting negative or reverse surge isabsorbed by the resistor 76 and the now lower resistance of theconducting tube 72. The tube 72 may be extinguished by momentarilyopening the reset switch 55. Similarly, the tubes 71 and 73 becomeignited upon opening of their associated contacts 26 and 28.

In the circuits of Figs. 3, 4, and 5, the simultaneous opening of anytwo or more of the contacts 26, 27, and 28 results in the ignition ofthe appropriate ones of the tubes 48, 49, and 50 or 71, 72, and 73. Inthe circuits of Figs. 3 and 4, should one of the contacts open after onehas already opened, the tube ignited by the opening of the first contactremains ignited. In other words, the annunciator remembers which contactopened first. In the circuit of Fig. 5, however, this memory ability isnot present, since the opening of any one of the contacts on thenegative side of the contact which first opened causes the ignited tubeto be extinguished.

Fig. 6 illustrates an annunicator similar to that of Fig. 3 but arrangedto indicate which of several contacts such as 91 and 92 in series withan operating winding of an electro-magnetic relay 94 might have openedto deenergize the relay 94, and which of several contacts such as 96,97, and 98 in series with an operating winding of an electromagneticrelay 99 might have opened to deenergize the relay 99. The relays 94 and99 may also be controlled by respective switches 100 and 101.

The annunciator of Fig. 6 comprises a plurality of three-element, coldcathode, gaseous discharge tubes 102 through 106 having their respectivetrigger electrodes connected in triggering circuits 102 through 106'.The triggering circuits 102 through 106 are identical with each otherand with the triggering circuits of Fig. 3 and are associated with thecontacts 96, 91, 92, 97, and 98, respectively. The cathode-platecircuits of the tubes 102 through 106 are completed in parallel from thenegative conductor 17 through the respective cathodes and plates andrespective resistors 68 to the junction point 56 between the resistors52 and 54.

In operation of the circuit of Fig. 6, opening of either or both of thecontacts 91 and 92 or any of the contacts 95, 96, and 98 causes ignitionof its associated one of the tubes 102 through 106 which by its glowindicates which of the contacts opened.

Fig. 7 is a fragmentary wiring diagram which illustrates how the otherannunciators described herein may be modified to be used with analternating current source.

Referring to Fig. 7, an electromagnetic contactor 110 which might serveto control an alternating current motor (not shown) by means of itsnormally open main contacts 110a has its operating winding 110wconnected between suitable alternating current supply conductors 111 and112 through a normally open start push button 114, a normally closedstop push button 115, a normally closed protective contact 116, and anormally open protective contact 118. A normally-open auxiliary contact110b is arranged to by-pass the push button 114 to provide a holdingcircuit for the contactor 110.

A plurality of transformers 119, 120, and 121 have their primarywindings 119p, 120p, and 121p, connected in loop circuits with the pushbutton 115 and the contacts 116 and 118, respectively, and have oneterminal of each of their secondary windings 119s, 120s, and 121sconnected to a negative terminal 128a of a full wave rectifier 128 andthe other terminals of their secondary windings connected, respectively,to trigger electrodes of respective three-element, cold cathode, gaseousdischarge tubes 122, 124, and 125 which may be the same as the tubes 48,49, and 50 of Figs. 3 and 4. A plurality of resistors 126 interposed inthe respective loop circuits have their ohmic values so selected withrespect to the impedance of the winding 110w, the impedance of theirassociated primary windings 119p, 120p, or 121p, and the highest voltageexpected between the conductors 111 and 112 that, upon opening of thepush button 115 or either of the contacts 116 and 118, the contactor 110drops out.

The cathode-plate circuits of the respective tubes 122, 124, and 125 areconnected in parallel with each other across direct current outputterminals 128a and 128b of the rectifier 128 which has its alternatingcurrent terminals connected between the conductors 111 and 112.Resistors 129 are interposed in the plate circuits, respectively, whichare controlled by a push button 130. A capacitor 131 serves to filterthe D.-C. output of of the rectifier 128.

Operation of the system of Fig. 7 is similar to that of Fig. 3, thevoltage that appears in the secondary windings 119s, 120s, and 121s uponopening of its associated push button 115 or contacts 116 and 118causing the appropriate one of the trigger electrodes to ignite itsassociated tube 122, 124, and 125.

in the electronic annunciator of Fig. 8, a plurality of two-element,cold cathode, gaseous discharge tubes 141, 142, and 143 which may besimilar to the tubes 71, 72, and 73 of Fig. have their respectivecathodes 141c, 1420, and 1430 connected to the negative conductor 17 andtheir respective plates 141p, 142p, and 143p connected throughrespective resistors 145 to a junction point 146. The junction point 146is connected through a normally closed push button or reset switch 148to an adjustable intermediate point 14911 on a resistor 149 which formspart of a voltage divider 150 also including a resistor 151 andconnected between the conductors 16 and 17 with the resistors 149 and151 in series. Thus the tubes 141, 142, and 143 are connected inparallel with each other across the resistor 151 and the right handportion of the resistor 149 and preferably are subjected to a potentialmidway between their ignition and extinction potentials.

The plate 141p is connected through a capacitor 154 to the positive sideof the contact 28, the plate 142p is connected through a capacitor 155to the positive side of the contact 27, and the plate 143p is connectedthrough a capacitor 156 to the positive side of the contact 26. Thepositive side of the contact 26 is arranged to be connected to thepositive conductor 16 through the winding 25w of the undervoltage relay25 and, in parallel, through the conductor 29 including the contact 25aand the conductor 24 which includes the off-point segment 22 as shown inFig. 3.

When conditions are normal and all of the contacts 26, 27, and 28 areclosed, the capacitors 154, 155, and 156 are charged to the voltageappearing across the resistor 151 and the right hand portion of theresistor 149 and none of the tubes 141, 142, and 143 is ignited. Uponopening of the contact 26, the relay 25 becomes deenergized and the sideof the contact 26 nearest to the relay winding 25w suddenly changes fromthe potential of the negative conductor 17 to that of the positiveconductor 16. Since the voltage across a capacitor cannot changeinstantaneously, there is a sudden increase in potential at the plate143p. The cathode 143C, however, remains at the potential of thenegative 10 conductor 17. This voltage difference is sufl'icient tocause the tube 143 to break down an emit a visible glow, and it remainsignited by the current flowing through its plate circuit and theassociated one of the resistors 145.

If the contact 27 opens instead of the contact 26, the relay 25 becomesdeenergized and the side of the contact 26 nearest the relay winding 25was well as the side of the contact 27 nearest the contact 26 suddenlychange from the potential of the negative conductor 17 to the potentialof the positive conductor 16. In this instance the tubes 142 and 143both become ignited. If the contact 28 opens instead of the contacts 26or 27, all three of the tubes 141, 142, and 143 become ignited.

The tubes 141, 142, and 143 are preferably arranged in a row as are thetubes 12 of Fig. 1 so that when but one of the tubes, for example, thetube 143, at one end of the row becomes ignited, it will be known thatthe contact 26 nearest the positive conductor 16 opened. If both of thetubes 142 and 143 become ignited, it will be known that the contact 27opened, and if all three of the tubes 141, 142, and 143 become ignited,it will be known that the contact 28 opened.

The ignited ones of the tubes 141, 142, and 143 may be extinguished atany time by opening the push button 148.

Although a preferred and several modified arrangements of apparatus andcircuits are disclosed herein, it is to be understood that such aremerely illustrative of the principles of the invention.

Having thus described my invention, I claim:

1. An electronic annunciator system comprising an electroresponsivedevice, control circuit means connecting said device across a source ofpower and including a plurality of contacts in series with each otherand in series with said device, a plurality of gaseous discharge tubeseach having a pair of electrodes across which a gaseous discharge whenonce initiated is maintained so long as a potential in excess of apredetermined minimum potential is impressed therebetween, plate circuitmeans connecting each of said pairs of electrodes to a source of powerindependently of said control circuit means and operative independentlyof the electrical condition of said control circuit means to impressbetween the electrodes of each tube a predetermined intermediatepotential which is in excess of said minimum potential but less than ahigher potential required to initiate a discharge between the electrodesof each tube, voltage transferring means connected to said tubes,respectively, and operative when subjected to a voltage above apredetermined value to initiate a discharge 7 between the pair ofelectrodes of its associated tube irrespective of the electricalcondition of any of the other ones of said tubes, and coupling meanselectrically associated with said contacts, respectively, and with saidvoltage transferring means, respectively, so that said tubes areelectrically associated with said contacts, respectively, said couplingmeans being operative upon opening of any of said contacts while saidcircuit means is connected to said source of power and carrying currentto subject the voltage transferring means associated with the openedcontact to a voltage above said predetermined value thereby to initiatea discharge which is capable of being maintained by said plate circuitmeans between the electrodes of each one of said tubes associated withan opened contact.

2. The electronic annunciator system of claim 1 characterized in thatsaid tubes constitute visible signals and have transparent envelopes andare so mounted that at least a portion of each of said envelopes isexposed to view.

3. The electronic annunciator of claim 2 characterized in that saidtubes are provided with indicia which relates each tube with the contactwith which it is electrically associated.

4. The electronic annunciator system of claim 1 characterized in thatsaid tubes are of the cold cathode type.

5. The electronic annunciator system of claim 1 characterized in thatsaid tubes are each of the threeelement, cold cathode type having atrigger electrode and each of said voltage transferring means isconnected to said trigger electrode and one of said other electrodes ofits associated tube in a circuit operatively isolated from all of theother voltage transferring means.

6. The electronic annunciator system of claim 5 characterized in thatsaid electroresponsive device includes an inductive winding, saidcontacts are connected in series with each other and in series with saidwinding and are all closed at the same time to energize said windingwhile said control circuit means is connected to its source of power,and said coupling means includes coupling circuits respective to saidcontacts and operative upon opening of its associated contact to subjectthe voltage transferring means associated with the opened contact to avoltage above said predetermined value.

7. The electronic annunciator system of claim 6 characterized in thatsaid electroresponsive device is an undervoltage relay.

8. The electronic annunciator system of claim 6 characterized in thateach of said voltage transferring means comprises a transformer havingits primary winding connected by its associated coupling circuit inparallel with its associated contact.

9. The electronic annunciator system of claim 8 characterized in thateach of said coupling circuits includes a resistor connected in serieswith its associated primary winding in a loop circuit with the contactassociated with its associated primary winding.

10. The electronic annunciator system of claim 8 characterized in thateach of said coupling circuits includes a capacitor connected in serieswith its associattd primary winding in a loop circuit with the contactassociated with its associated primary winding.

11. The electronic annunciator system of claim 1 characterized in thatsaid tubes are of the two-element, cold cathode types, each of saidvoltage transferring means comprises a capacitor, and the associated oneof said coupling means connects its capacitor in a loop circuitincluding its associated contact and tube.

12. An undervoltage protection system comprising an electromagneticundervoltage relay having an operating winding, an undervoltage relaycircuit including said winding and adapted to be connected across asource of power for energizing said winding from the source, a pluralityof contacts connected in series with each other in said undervoltagerelay circuit and in series with said winding, means maintaininig all ofsaid contacts in closed position for effecting energization of saidwinding upon connection of said undervoltage relay circuit across thesource of power, means for opening said contacts selectively to effectdeenergization of said winding, a plurality of gaseous discharge tubeseach having a pair of principal electrodes and a transparent envelopeand capable of emitting a visible glow when current is flowing acrosssaid electrodes, plate circuit means connecting each of said pair ofelectrodes to a source of power independently of said undervoltage relaycircuit and operative independently of the electrical condition of saidundervoltage relay circuit to impress a voltage across each pair of saidelectrodes, firing means for said tubes, respectively, and eachoperative to initiate conduction of its associated tube irrespective ofthe electrical condition of any other tube, and means operativelyassociating said firing means with said contacts, respectively, in amanner such that the conductivity or non-conductivity of said tubesdepends upon whether its associated contact is open or closed.

13. An undervoltage protection system comprising an electromagneticundervoltage relay having an operating winding, a circuit meansincluding said winding and adapted to be connected across a source ofpower for energizing said winding from the source, a plurality ofcontacts connected in series with each other in said circuit means inseries with said winding, means maintaining all of said contacts inclosed position for effecting energization of said winding uponconnection of said circuit means across the source of power, means foropening said contacts selectively to effect deenergization of saidwinding, a plurality of transformers each having a primary and asecondary winding, coupling means connecting said primary winding acrosssaid contacts, respectively, a plurality of three-element, cold cathode,gaseous discharge tubes each having an anode, a cathode, and a triggerelectrode, plate circuit means independent of said circuit means andrespective to said tubes and operatively isolated each from the other ina manner such that conduction and non-conduction of a tube has no elfecton any other tube, each of said plate circuit means connecting the anodeand cathode of its associated tube to a source of power independently ofsaid circuit means and operative independently of the electricalcondition of said control circuit means to impress across the anode andcathode of its associated tube a potential which is less than thepotential required to initiate a discharge between the anode and cathodethereof but sufficient to maintain said discharge, means connecting oneterminal of each of said secondary windings to said trigger electrodes,respectively, and means connecting the other terminals of said secondarywindings to each other and to said cathodes.

14. The undervoltage protection system of claim 13 characterized in thatresistors are interposed in said coupling means respectively, theresistance of said resistors being so related to the voltage of thesource and the resistance of said primary windings and said relaywinding that opening of any of said contacts while said circuit means isconnected to said source causes said relay to drop out.

15. The undervoltage protection system of claim 14 characterized in thatsaid relay is an alternating current relay, said circuit means isadapted to be connected across a source of alternating current, and arectifier arranged to be connected to said source has its direct currentterminals connected to said anodes and said cathodes, respectively.

l6. The undervoltage protection system of claim 13 characterized in thatsaid coupling means includes capacitors, respectively.

17. An undervoltage protection system comprising an electromagneticundervoltage relay having an operating winding, acircuit including saidwinding and having positive and negative terminals adapted to beconnected across a source of direct current power for energizing saidwinding from the source, a plurality of contacts connected in serieswith each other in said circuit means in series with said windingbetween said winding and said negative terminal, means maintaining allof said contacts in closed position for efiecting energization of saidwinding upon connection of said circuit means across the source ofpower, means for opening said contacts selectively to efiectdeenergization of said winding, a plurality of cold cathode, gaseousdischarge tubes each having an anode and a cathode, a plurality ofcapacitors, means connecting said anodes through said capacitors,respectively, to the sides, respectively, of said contacts nearest saidpositive terminal, and plate circuit means including means connectingsaid cathodes to said negative terminal and connected to said anodes andcathodes independently of said circuit, Said plate circuit means beingoperative when energized to impress a potential across the anode andcathode of each tube which is less than the potential required toinitiate a discharge between the anode and cathode thereof butsufficient to maintain said discharge.

18. The undervoltage protection system of claim 17 characterized in thatsaid means connecting said cathodes to said negative terminal connectseach of said cathodes to the side of its associated contact that isnearest said negative terminal.

References Cited in the file of this patent UNITED STATES PATENTSLivingston Oct. 13, 1936 Edgerton Aug. 16, 1949 Walz June 26, 1951Cochran Nov. 27, 1951 Foote et a1. Oct. 14, 1952 FOREIGN PATENTS GreatBritain June 22, 1942

